Reading an article about the Skins picking up the 5th year, $16M option on RG3, and saw something that surprised me

So they rolled the dice with $16 million for 2016 in order to avoid having to pay roughly $20 million or more, if Griffin becomes the guy in 2015 that he was in 2012. And if he stinks, the smart move will be to yank him from the field, ensconce him in bubble wrap, and then cut him in the offseason before that $16 million becomes fully guaranteed next March.
I thought the 5th year option was fully guaranteed (injury and skill) when it was exercised.